Shader:sendColor and shader:send call the exact same internal base function. The only differences are that sendColor divides input values by 255 (to match GLSL's [0-1] range for colors) whereas Shader:send doesn't so you should give color values that are already within [0-1] rather than [0-255] if you use Shader:send, and sendColor performs gamma correction if applicable, whereas send does not.